Motion control unit for vehicle based on jerk information

ABSTRACT

In a motion control system for a vehicle including control means for controlling a yaw moment of the vehicle; first detection means for detecting a longitudinal velocity (V) of the vehicle; second detection means for detecting a lateral jerk (Gy_dot) of the vehicle; and third detection means for detecting a yaw angular acceleration (r_dot) of the vehicle, the yaw moment of the vehicle is controlled by the control means so that a difference between the yaw angular acceleration (r_dot) detected by the third detection means and a value (Gy_dot/V) obtained by the lateral jerk (Gy_dot) of the vehicle detected by the second detection means by the longitudinal velocity (V) detected by the first detection means becomes small.

This application is a continuation of U.S. application Ser. No.13/339,997, filed Dec. 29, 2011, which is a continuation of U.S.application Ser. No. 13/151,904, filed Jun. 2, 2011 which is acontinuation of U.S. application Ser. No. 12/121,323, filed May 15, 2008which claims priority from Japanese application serial No. 2007-132987,filed on May 18, 2007, the contents of which are hereby incorporated byreference into this application in their entirety.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a system for performing a motioncontrol of a vehicle, and more particularly, to a system for controllinga yaw moment based on lateral jerk information.

(2) Description of Related Art

A vehicle control system for controlling a yaw moment of the vehicle isdisclosed in, for example, JP-A-10-16599. Here, in general, a torquedifference is generated between left and right wheels of the vehicle soas to unbalance left and right drive forces or brake forces generatedbetween a road surface and the left and right wheels, thereby generatingthe yaw moment of the vehicle to control the movement of the vehicle.

As to control logic for determining a target value of a torquedifference generated between the left and right wheels of the vehicle,JP-A-10-16599 discloses a method for setting the target value of thetorque difference to a value proportional to a handle angular velocity.According to JP-A-10-16599, if the torque difference proportional to thehandle angular velocity is generated, the yaw moment proportional to thehandle angular velocity is generated, to improve the initial responseperformance of the yaw moment of the vehicle with respect to a handleoperation.

BRIEF SUMMARY OF THE INVENTION

However, like the control logic disclosed in JP-A-10-16599, when thetarget value of the torque difference generated between the left andright wheels of the vehicle is set to the value proportional to thehandle angular velocity, it is not possible to surely handle a variationin dynamics (lateral motion performance of the vehicle) of the vehicle.

In a case where yaw response stability deteriorates due to a highvelocity of the vehicle, a tire arrives at a nonlinear area in a lateralskid state of the vehicle, a load of each wheel varies due to anacceleration, or a lateral force is reduced due to an increase inlongitudinal force of the tire, an original restoration yaw moment ofthe vehicle varies. Due to a composition yaw moment of the restorationyaw moment and a control input, the vehicle will be unstable in somesituation.

An object of the invention is to provide a motion control system for avehicle capable of varying a yaw moment control amount in accordancewith a variation in dynamics of the vehicle.

In order to solve the above-described problems, the present inventionmainly adopts the following configuration.

In a motion control system for a vehicle including: control means forcontrolling a yaw moment of the vehicle; first detection means fordetecting a longitudinal velocity (V) of the Vehicle; and seconddetection means for detecting a lateral jerk (Gy_dot) of the vehicle,the yaw moment of the vehicle is controlled on the basis of a value(Gy_dot/V) obtained by dividing the lateral jerk (Gy_dot) of the vehicledetected by the second detection means by the longitudinal velocity (V)of the vehicle detected by the first detection means.

In addition, in the motion control system for the vehicle furtherincluding third detection means for detecting a yaw angular acceleration(r_dot) of the vehicle, the yaw moment of the vehicle is controlled bythe control means so that a difference between the yaw angularacceleration (r_dot) of the vehicle detected by the third detectionmeans and the value (Gy_dot/V) obtained by dividing the lateral jerk(Gy_dot) of the vehicle by the longitudinal velocity (V) of the vehiclebecomes small.

According to the invention, since the control yaw moment amount can becontrolled in accordance with ea variation in lateral dynamics of thevehicle including an transient acceleration or deceleration state of thevehicle, it is possible to realize a stable driving.

Other objects, features, and advantages of the invention will be, orwill become, apparent in the detailed description of the invention basedon the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a view illustrating an overall configuration of a motioncontrol system for a vehicle.

FIGS. 2A to 2D are schematic views illustrating a state where threetypes of positive yaw moment inputs are carried out when a vehicle turnsin a counterclockwise direction. FIG. 2A is a schematic viewillustrating a steady state cornering, FIG. 2B is a schematic viewillustrating a state where a positive moment is added in terms of asteering operation, FIG. 2C is a schematic view illustrating a statewhere a positive moment is added by a left and right differential brakeand drive input, and FIG. 2D is a schematic view illustrating a statewhere a positive moment is added by a vertical load transfer from a rearwheel to a front wheel in terms of a braking operation.

FIGS. 3A to 3D are schematic views illustrating a state where threetypes of negative yaw moment inputs are carried out when a vehicle turnsin a counterclockwise direction. FIG. 3A is a schematic viewillustrating a steady state cornering, FIG. 3B is a schematic viewillustrating a state where a negative moment is input in terms of thesteering operation, FIG. 3C is a schematic view illustrating a statewhere a negative moment is added by the left and right differentialbrake and drive input, and FIG. 3D is a schematic view illustrating astate where a negative moment is added by a vertical load transfer froma rear wheel to a front wheel in terms of the braking operation.

FIG. 4 is a diagrammatic view illustrating a concept of a curvature of alocus and an arc length along the locus for showing a case where avehicle turns along a curve.

FIGS. 5A to 5B are views illustrating an ideal state where a vehicleturns without a sideslip. FIG. 5A is a schematic view illustrating astate without a sideslip angle and FIG. 5B is a schematic viewillustrating a state with a sideslip angle.

FIG. 6 is a view illustrating a state where a real vehicle havingdynamical cornering characteristics and a state where a control yawmoment is necessary.

FIG. 7 is a diagrammatic view illustrating control logic in the motioncontrol system for the vehicle.

FIG. 8 is a diagrammatic view illustrating real measurement results ofacceleration or deceleration motions in a vehicle.

FIG. 9 is a diagrammatic view illustrating real measurement results of areference yaw angular acceleration and a real yaw angular accelerationwhen a vehicle velocity and a steering condition are determined.

FIG. 10 is a diagrammatic view illustrating real measurement results ofa target yaw moment and a correction yaw moment when the vehiclevelocity and the steering condition are determined.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a motion control system for a vehicle will be described indetail with reference to FIGS. 1 to 10. FIG. 1 is a view illustrating anoverall configuration of a motion control system for a vehicle. In thisembodiment, a vehicle 0 is configured as a so-called by-wire-system, inwhich a mechanical connection does not exist among a driver, a steeringmechanism, an acceleration mechanism, and a deceleration mechanism.Next, a configuration and an operation of the motion control system forthe vehicle according to this embodiment will be described in each itemthereof.

<Driving>

The vehicle 0 is a rear wheel driven vehicle (Rear Motor Rear Driver: RRvehicle) (a drive type is not directly involved with this embodiment). Adrive force distributing mechanism 2 connected to a motor 1 is mountedtherein so as to be capable of freely distributing torque from the motorto left and right wheels.

First, a detailed system configuration will be described. A left frontwheel 61, a right front wheel 62, the left rear wheel 63, and the rightrear wheel 64 are respectively mounted with a brake rotor and a vehiclewheel velocity detecting rotor(encorder), and a vehicle body is mountedwith a vehicle velocity pickup, thereby being configured to detect avehicle wheel velocity of each vehicle wheel. An amount that the driverpresses an accelerator pedal 10 is detected by an accelerator positionsensor 31 and is calculated by a central control 40 via a pedal control48. In this calculation process, torque distribution information isincluded in accordance with a yaw moment control according to thisembodiment. Then, a powertrain controller 46 controls an output of themotor 1 in accordance with the control amount. In addition, the outputof the motor 1 is distributed to the left rear wheel 63 and the rightrear wheel 64 at an appropriate ratio via the drive force distributingmechanism 2 controlled by the powertrain controller 46.

The accelerator pedal 10 is connected to an accelerator reaction motor51 and a reaction control is carried out by the pedal controller 48 onthe basis of a calculation command of the central controller 40.

<Braking>

The left front wheel 51, the right front wheel 52, the left rear wheel53, and the right rear wheel 54 are respectively provided with the brakerotor, and the vehicle body is mounted with calipers for deceleratingthe vehicle wheels by interposing the brake rotor between pads (notshown). The calipers are of a hydraulic type or an electric type inwhich each caliper has an electric motor.

Each caliper is basically controlled by a brake controller 451 (for thefront wheel) and 452 (for the rear wheel) on the basis of thecalculation command of the central controller 40. In addition, asdescribed above, each vehicle wheel velocity is input to the brakecontrollers 451 and 452. An absolute vehicle velocity can be estimatedby averaging the vehicle wheel velocity of the front wheel (non-drivingwheel) from the vehicle wheel velocities of the four wheels.

In this embodiment, by using a signal of an acceleration sensor fordetecting the vehicle wheel velocity and the longitudinal accelerationof the vehicle, even when the vehicle wheel velocities of the fourwheels decrease at the same time, the absolute vehicle velocity (V) canbe measured accurately (such an absolute vehicle velocity can bemeasured, for example, by the technique disclosed in JP-A-05-16789 andthe like). In addition, by obtaining a difference between the left andright vehicle wheel velocities of the front wheel (non-driving wheel), ayaw rate of the vehicle body is estimated (r_w). Then, the signal ascommon information is monitored in the central controller 40 at a normaltime.

A brake pedal 11 is connected to a brake reaction motor 52, and areaction control is carried out by the pedal controller 48 on the basisof the calculation command of the central controller 40.

<Overall Control of Braking and Driving>

In this embodiment, there is provided three modes (as described below,Yaw Moment Addition in terms of Steering Operation, Yaw Moment Additionin terms of Left and Right Differential Brake and Drive Input, and YawMoment Addition in terms of Load Transfer from Front Wheel to Rear Wheel(see FIG. 7)) for realizing a yaw moment control described below, andone of them is ‘Yaw Moment Addition in terms of Left and RightDifferential Brake and Drive Input’. Although a different brake force ordrive force is generated in the left and right vehicle wheels, adifference between the left and right brake forces or drive forces leadsto the yaw moment.

Accordingly, in order to realize the difference, an operation, in whicha drive operation is performed on one side and a brake operation isperformed on the other side, different from a general operation may becarried out. In such a circumstance, an overall control command isoverall determined by the central controller 40, and the control isadequately carried out in terms of the brake controller 451 (for thefront wheel) and 452 (for the rear wheel), the powertrain controller 46,the motor 1, and the drive force distribution mechanism 2.

<Steering>

A steering system of the vehicle 0 is configured as a four wheelsteering system, a steer-by-wire structure without a mechanicalconnection between a steering angle of the driver and a turning angle ofa tire. The steering system includes a front power steering 7 havingtherein a steering angle sensor (not shown), a steering 16, a driversteering angle sensor 33, and a steering controller 44. An amount thatthe steering 16 is steered by the driver is detected by the driversteering angle sensor 33 and a calculation process is carried out by thecentral controller 40 via the steering controller 44. In the calculationprocess, the steering angle input in accordance with the yaw momentcontrol according to this embodiment is included. Then, the steeringcontroller 44 controls the front power steering 7 and the rear powersteering 8 in accordance with the steering amount.

The steering 16 is connected to the steering reaction motor 53, and areaction control is carried out by the steering controller 44 on thebasis of the calculation command of the central controller 40. An amountthat the driver presses the brake pedal 11 is detected by a brake pedalposition sensor 32, and a calculation process is carried out by thecentral controller 40 via the pedal controller 48.

<Sensor>

Next, a motion sensor group according to this embodiment will bedescribed. As shown in FIG. 1, a lateral acceleration sensor 21, alongitudinal acceleration sensor 22, and a yaw rate sensor 38 (arotation angular velocity of the vehicle) are arranged around a gravitycenter point of the vehicle. In addition, differential circuits 23 and24 are mounted therein so as to obtain jerk information bydifferentiating the outputs of the respective acceleration sensors. Adifferential circuit 25 is mounted therein so as to obtain a yaw angularacceleration signal by differentiating the output of the yaw rate sensor38.

In this embodiment, although the differential circuits are depicted tobe installed in each sensor so as to make sure the existence of thedifferential circuits, the differential process may be carried out afterthe acceleration signals are directly input to the central controller 40so as to perform various calculation processes. Accordingly, the yawangular acceleration of the vehicle body may be obtained by performingthe differential process in the central controller 40 using theestimated yaw rate obtained from the front vehicle wheel velocitysensor. In addition, although the acceleration sensor and thedifferential circuit are used to obtain a jerk, an already known jerksensor (for example, see JP-A-2002-340925) may be used.

<Yaw Moment Controlling>

Next, the yaw moment control in terms of a drive force distribution tothe left and right vehicle wheels will be described with reference toFIGS. 2A to 2D and FIGS. 3A to 3D. In this embodiment, the yaw momentapplied to the vehicle 0 is controlled by using three methods of ‘YawMoment Addition in terms of Steering Operation’, ‘Yaw Moment Addition interms of Left and Right Differential Brake and Drive Input’, and ‘YawMoment Addition in terms of Vertical Load Transfer from Front Wheel toRear Wheel’. FIGS. 2A to 2D are schematic views illustrating a statewhere three types of positive yaw moment inputs are carried out when avehicle turns in a counterclockwise direction. FIGS. 3A to 3D areschematic views illustrating a state where three types of negative yawmoment inputs are carried out when a vehicle turns in a counterclockwisedirection.

FIGS. 2A to 2D are views illustrating three methods upon inputting thepositive yaw moment from the standard state shown in FIG. 2A. First, alateral motion equation and a yawing (rotation) motion equation of thevehicle 0 in the standard state shown in FIG. 2A are expressed.mG _(y) =F _(yf) +F _(yr)  [Equation 1]M=I _(z) {dot over (r)}=0=F _(yf) l _(f) −F _(yr) l _(r)  [Equation 2]Here, m: a mass of the vehicle 0, Gy: a lateral acceleration applied tothe vehicle 0, Fyf: a lateral force of the two front wheels, Fyr: alateral force of the two rear wheels, M: a yaw moment, Iz: a yawinginertia moment of the vehicle 0, r_dot: a yaw angular acceleration ofthe vehicle 0 (r denotes a yaw rate), lf: a distance between the gravitycenter point of the vehicle 0 and a front axle, and lr: a distancebetween the gravity center point of the vehicle 0 and a rear axle. Inthe standard state, the yawing motion is balanced (yaw moment is zero),and the angular acceleration is zero.

FIG. 2B is a state where ‘Yaw Moment Addition in terms of SteeringOperation’ is carried out from the standard state shown in FIG. 2A.Since the front wheel steering angle increases by Δδf and the rear wheelsteering angle increases by Δδr compared with the steady state corneringshown in FIG. 2A, the lateral force of the two front wheels increasesfrom Fyf to Fysf and the lateral force of the two rear wheels decreasesfrom Fyr to Fyrf, and according to Equation 2, the positive moment (Ms)is generated as the following Equation 3.M _(z)=(F _(yzf) l _(f) −F _(ybr) l _(r))−(F _(yzr) l _(f) −F _(yr) l_(r))=(l _(f) ΔF _(yzf) +l _(r) ΔF _(yzr))>0In addition, in this embodiment, although the four wheel steeringvehicle capable of steering the rear wheel is supposed, the positivemoment can be generated from a general front wheel steering vehicle.

Next, FIG. 2C is a state where ‘Yaw Moment Addition in terms of Left andRight Differential Brake and Drive Input’ is carried out from thestandard state shown in FIG. 2A, in which a brake force −Fdrl is appliedto the left rear wheel 63, a drive force Fdrr is applied to the rightrear wheel 64, and a brake force −Fdf is applied to the left front wheel61. In this case,

$\begin{matrix}{M_{d} = {{{F_{yf}l_{f}} - {F_{yr}l_{r}} + {\frac{d}{2}\left( {F_{drl} + F_{drr} + F_{df}} \right)}} > 0}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$Here, d denotes a tread (distance between the left and right vehiclewheels as shown in the drawing). In addition,F _(drl) +F _(drr) +F _(df)=0  [Equation 5]When the control is carried out in this way, the yaw moment can begenerated without generating the longitudinal acceleration ordeceleration other than the front wheel driven vehicle (in this example,without driving the right front wheel 62). That is, the yaw moment canbe added without giving an unpleasant feeling to the driver.

Next, FIG. 2D is a method in which a vertical load transfer ispositively generated from the rear wheel to the front wheel by applyingthe brake force and an original restoration yaw moment of the vehiclereduces, thereby generating the yaw moment.

The phenomenon of the yaw moment addition in terms of the vertical loadtransfer is such that the yaw moment due to the acceleration ordeceleration during a steady state cornering action is proportional to avalue obtained by multiplying the lateral force by the longitudinalacceleration within a range in which the lateral force of the tire isproportional to the vertical load as disclosed in p. 54 to 60 of‘improvement of Vehicle Motion Performance in terms of Yaw MomentControl’ written by SHIBAHATA et al. and published by ‘SOCIETY OFAUTOMOTIVE ENGINEERS OF JAPAN, INC., Vol. 47, No. 12, 1993.’ Thephenomenon occurs when a friction circle of the front wheel increases inaccordance with the deceleration −GX and a friction circle of the rearwheel decreases in accordance with the deceleration −GX from the stateshown in FIG. 2A. Here, −Gx is

$\begin{matrix}{G_{x} = {\frac{1}{m}\left( {{2\; F_{bf}} + F_{br}} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$Although the deformation of Equations is omitted until the input yawmoment becomes a value obtained by multiplying the lateral force by thelongitudinal acceleration,M _(d)=(F _(ybf) l _(f) −F _(ybr) l _(r))−(F _(yf) l _(f) −F _(yr) l_(r))=(l _(f) ΔF _(ybf) +l _(r) ΔF _(ybr))>0is obtained, and the positive yaw moment can be input.

Meanwhile, FIGS. 3A to 3D are methods in which the negative yaw momentis input in the same way as those shown in FIGS. 2A to 2D. Although thedetailed description is omitted because the method is the same as thatof the positive yaw moment input method shown in FIGS. 2A to 2D, themoment in the restoration direction (clockwise direction shown in FIGS.3B, 3C, and 3D) is obtained in such a manner that the steering operationis carried out so that the steering angle decreases or the steeringoperation is carried out so that a phase of the rear wheel becomes thesame as that of the front wheel, the brake or drive operation is carriedout so that an inverse brake or drive force is applied, the loadmovement is carried out so that an acceleration is performed to increasea load of the rear wheel, the lateral force of the rear wheelcomparatively increases, and the lateral force of the front wheeldecreases.

As described above, the vehicle according to this embodiment cangenerate both the positive and negative yaw moment on the basis of thecommand of the central controller 40.

Next, a yaw moment calculation method for a specific yaw moment commandwill be described in detail. In addition, an outline of theabove-described yaw moment generation method is introduced in variousdocuments.

<Technical Background of Vehicle Motion Dynamics>

As shown in FIG. 4, this corresponds to a state where the vehicle turnsalong a certain curve. In a curve of C(s)=(X(s), Y(s)) of the coordinatesystem (X, Y) fixed to a ground, s denotes a distance along the curve.When a curvature of a locus is denoted by κ(=1/ρ(ρ: turning radius)),generally κ is shown by using an arc length parameter (s) along thelocus as shown in Equation 8.

$\begin{matrix}{{\kappa(s)} = {\frac{1}{\rho(s)} = \frac{\mathbb{d}\theta}{\mathbb{d}s}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$That is, when a variation in angle (dθ) occurs upon moving along thecurve by a certain distance (ds), the variation is called a curvatureκ(dθ/cs).

As it is well known, a locus of the vehicle when a handle is steered ata stable angular velocity during a stable vehicle velocity is called aclothoid curve which is often used for designing a road. This curve is

$\begin{matrix}{\frac{\mathbb{d}{\kappa(s)}}{\mathbb{d}s} = {{\frac{\mathbb{d}}{\mathbb{d}s}\frac{\mathbb{d}\theta}{\mathbb{d}s}} = {\frac{\mathbb{d}^{2}\theta}{\mathbb{d}s^{2}} = {{const} = \kappa_{crothoid}}}}} & \left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack\end{matrix}$A variation rate of this curve is uniform with respect to the movementdistance. Accordingly, when the vehicle travels along the clothoid curveat a uniform velocity (u),

$\begin{matrix}{u = {\frac{\mathbb{d}s}{\mathbb{d}t} = {const}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$A time variation of the curvature of the vehicle becomes stable (whichmay be supposed that the arc length parameter changes to the timeparameter t).

$\begin{matrix}{\frac{\mathbb{d}{\kappa(s)}}{\mathbb{d}t} = {{\frac{\mathbb{d}s}{\mathbb{d}t}\frac{\mathbb{d}{\kappa(s)}}{\mathbb{d}s}} = {{u \cdot \kappa_{crothoid}} = {const}}}} & \left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack\end{matrix}$Meanwhile, from the definition of the curvature κ, κ(s) is expressed byEquation 12.

$\begin{matrix}{{\kappa(s)} = {\frac{1}{\rho(s)} = {\left. \frac{\mathbb{d}\theta}{\mathbb{d}s}\Rightarrow\theta \right. = {\psi_{({{Yaw}^{*}{\_ Angle}})} = {{\int_{s_{1}}^{s_{2}}{{\kappa(s)}{\mathbb{d}s}}} = {\int_{t_{1}}^{t_{2}}{{\kappa(t)}\frac{\mathbb{d}s}{\mathbb{d}t}{\mathbb{d}t}}}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$This means that the vehicle yaw angle ψ is generated when the vehiclemoves along the curve of the curvature κ(s) from s1 to s2 without avariation in sideslip.

As shown in FIGS. 5A to 5B, the state without a variation in sideslipindicates a state where a difference between a vector (V) in a directionperpendicular to the curve (bold black curve indicating C(s)) and avehicle velocity direction (direction indicated by the dashed line) iszero (FIG. 5A) or a state where an angle (β) called a sideslip angle isstable (FIG. 5B), which is considered as an ideal state where arevolution and a rotation of the vehicle cooperatively correspond toeach other. In addition, the yaw angle generated in the ideal state isdetermined geometrically and is not directly involved with the vehicledynamics. The details shown in FIGS. 5A to 5B are described in, forexample, ‘Vehicle dynamics and control’ written by ABE Masato andpublished by Sankaido, First edition, Jul. 10, 1992, Third chapter.

<Deduction of Reference Yaw Moment>

When time t1 to t2 is taken to move from s1 to s2 as shown in FIG. 4,the yaw rate r_ref of the vehicle in such a motion state is

$\begin{matrix}{{\therefore r_{ref}} = {\frac{\mathbb{d}\psi}{\mathbb{d}t} = {\frac{\mathbb{d}\theta}{\mathbb{d}t} = {{\frac{\mathbb{d}s}{\mathbb{d}t}\frac{\mathbb{d}\theta}{\mathbb{d}s}} = {{u(t)}{\kappa(t)}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$In addition, when the yaw angular acceleration r_ref_dot) is obtained,

$\begin{matrix}{{\therefore{\overset{.}{r}}_{ref}} = {{\frac{\mathbb{d}}{\mathbb{d}t}\left( {{u(t)}{\kappa(t)}} \right)} = {{{\overset{.}{u}(t)}{\kappa(t)}} + {{u(t)}{\overset{.}{\kappa}(t)}}}}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$Here, a velocity in a direction where the vehicle moves is as belowu(t)=V  [Equation 15]When the longitudinal acceleration of the vehicle is denoted by Gx,{dot over (u)}(t)={dot over (V)}=G _(x)  [Equation 16]In addition, when the lateral acceleration of the vehicle is denoted byGy, as shown in FIGS. 5A to 5B, the vehicle moving in a state where avariation in sideslip does not occur has a relationship

$\begin{matrix}{{{r(t)} = \frac{G_{y}}{V}}{and}} & \left\lbrack {{Equation}\mspace{14mu} 17} \right\rbrack \\{{\kappa(t)} = \frac{G_{y}}{V^{2}}} & \left\lbrack {{Equation}\mspace{14mu} 18} \right\rbrack\end{matrix}$When the time variation of the curvature is obtained by differentiatingboth sides,

$\begin{matrix}{{\overset{.}{\kappa}(t)} = {\frac{{{\overset{.}{G}}_{y}V^{2}} - {G_{y}2\; V\overset{.}{V}}}{V^{4}} = \frac{{{\overset{.}{G}}_{y}V} - {2\; G_{y}G_{x}}}{V^{3}}}} & \left\lbrack {{Equation}\mspace{14mu} 19} \right\rbrack\end{matrix}$Here, Gy_dot denotes the lateral jerk of the vehicle. When Equations 16,18, and 19 are applied to Equation 14,

$\begin{matrix}\begin{matrix}{{\therefore{\overset{.}{r}}_{ref}} = {{{{\overset{.}{u}(t)}{\kappa(t)}} + {{u(t)}{\overset{.}{\kappa}(t)}}} = {{G_{x}\frac{G_{y}}{V^{2}}} +}}} \\{V\frac{{{\overset{.}{G}}_{y}V} - {2\; G_{y}G_{x}}}{V^{3}}} \\{= {{\frac{{\overset{.}{G}}_{y}}{V} - \frac{G_{x}G_{y}}{V^{2}}} \approx \frac{{\overset{.}{G}}_{y}}{V}}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 20} \right\rbrack\end{matrix}$Here, since a value obtained by dividing a value, obtained bymultiplying the longitudinal acceleration by the lateral acceleration,by a square of the velocity in a second term is smaller than that of afirst term, this is not considered in this embodiment. This may beconsidered when higher precise value is required.

Then, Equation 20 shows the yaw angular acceleration necessary for thevehicle moving in the ideal state. When the value of the yaw angularacceleration is multiplied by the yawing inertia moment Iz of thevehicle, the reference yaw moment is obtained (which generallycorresponds to a relationship of a force f=m×acceleration α).

<Control Logic>

Next, a method for controlling the yaw moment of the vehicle being in arunning state using the above-described reference yaw moment will bedescribed. Here, the reference moment indicates a moment necessary formoving along the path in a state where the revolution and the rotationof the vehicle are cooperatively correspond to each other as shown inFIGS. 5A to 5B. When the moment is large, the vehicle rotates, and whenthe moment is small, the vehicle deviates from the path.

As shown in FIG. 6, a separation occurs in revolving motion and rotatingmotion of the real vehicle. This is because a characteristic of thevehicle varies in accordance with a variation in velocity, a variationin vertical load distribution, the disturbance, and the like. In thisembodiment, correcting this separation (deviation shown in FIG. 6) isconsidered. Specifically, the following two are supposed. A firstsupposition is to correct a case that the lateral acceleration withrespect to the yaw rate has a response delay as a variation amount ofthe sideslip angle in a transition state where the vehicle moving alonga line performs a turning action or the vehicle performing the turningout action from a curved line (turning in and turning out assist).Another supposition is to restrict a case that lateral forces balance ofthe front and rear wheels is broken due to a certain reason so that therotation more increases than the revolution (spin) (anti spin control).

An output angular acceleration obtained by the differential circuit 25from the yaw rate obtained from the yaw rate sensor 38 mounted in thevehicle 0 or estimated by a difference between the left and rightvehicle wheel velocity sensors is denoted by r_real_dot. When this valueis multiplied by the yaw rate inertia moment Iz of the vehicle 0, it ispossible to obtain the yaw moment acting on the current vehicle.

Consequently, a difference between the action yaw moment (Iz·r_real_dot)and the reference yaw moment (Iz·r_ref_dot) corresponds to a differentyaw moment as a cause of the separation of the revolution and therotation. Accordingly,ΔM=k·I _(z)({dot over (r)} _(ref) −{dot over (r)} _(real))  [Equation21]This is the yaw moment to be corrected. Here, k denotes a proportionalgain. The reason why the proportional gain is necessary is that thereference yaw moment does not include the dynamics, and when a directfeedback (k=1) is applied thereto, there exists a divergence area.Accordingly, k needs to be adjusted necessarily so as to be 1 or less.<Configuration of Control Logic>

FIG. 7 is a schematic view illustrating the configuration of the controllogic according to this embodiment. The yaw moment of the vehicle isconfigured to be controlled on the basis of a value (Gy_dot/V) obtainedby dividing the lateral jerk Gy_dot of the vehicle by the longitudinalvelocity (V) of the vehicle. The yaw moment of the vehicle is configuredto be controlled so that a difference between (Gy_dot/V) and (r_dot)becomes small by detecting the yaw angular acceleration (r_dot) of thevehicle.

In addition, a selection or a combination of ‘Yaw Moment Addition interms of Steering Operation’, ‘Yaw Moment Addition in terms of Left andRight Differential Brake and Drive Input’, and ‘Yaw Moment Addition interms of Load Movement from Front Wheel to Rear Wheel’ is determined inaccordance with the driver's input. For example, when there is anaccelerator input, ‘Yaw Moment Addition in terms of Vertical LoadTransfer from Front Wheel to Rear Wheel’ which causing a deceleration isnot carried or a total sum of ‘Left and Right Differential Brake andDrive Input’ is controlled in accordance with the driver's acceleratorinput. The series of processes are carried out by the central controller40.

<Principle Justification Verification by Real Detection Result>

Next, a detection examination result of a correction yaw moment ΔM usingthe real vehicle is shown. The examination vehicle is a front-enginefront-drive passenger car having a mass of about 1,500 [kg] and a yawinginertia moment of 2,500 [kgm²], and has a lateral jerk detecting meansand a yaw angular acceleration detecting means.

FIG. 8 shows a locus (measurement value) of the vehicle, thelongitudinal acceleration of the vehicle, the lateral acceleration ofthe vehicle, the reference yaw angular acceleration r_ref_dot obtainedby dividing the lateral acceleration at that time by the velocity, theyaw angular acceleration r_real_dot of the real vehicle, and adifference between the respective angular accelerations when the driverperforms a line trace task (on the left side in the drawing, (d)→(a))and a voluntary drive (on the left side, (b)→(d)) in which the path isfreely selected. A line to be traced is painted on a road surface on theleft side of approximately X=−100 [m] of a test track.

Accordingly, the driver approaches from a side of X=0 [m] to a rightcorner. A moment indicating an escape from the left corner correspondsto positions around 75 [s(Time)] in the below two graphs, and a task issuch that the vehicle enters a corner (b) from this position, escapesfrom a corner (c), and again enters a corner (d).

Although a velocity just before entering the line trace task (left)corner is approximately set to be 60 [km/h], the driver may use freelythe brake and the accelerator. This corresponds to the secondacceleration graph of FIG. 8. Accordingly, it is necessary to payattention that this test is a result in accordance with a freeacceleration.

As it may be estimated from Equation 20, the yaw angular acceleration ishighly relevant with the time variation of the curvature κ. Accordingly,the reference yaw angular acceleration is generated at a corner entranceto trace a line of which the curvature varies. As shown in the thirddrawing of FIG. 8, a difference between the reference yaw angularacceleration and the real yaw angular acceleration is very little, andthe driver traces the line by accurately controlling the vehicle.

Here, the downmost drawing of FIG. 8 shows the correction yaw moment.Although the amount is little as a whole, the value is positive when thereference yaw angular acceleration increases up to a peak and the valueis negative when the reference yaw angular acceleration decreases. It isobvious that immediate response performance and convergence performanceof the vehicle motion can be improved in such a manner that as shown inEquation 21, this value is fed back by multiplying an adequate gain kthereto and the yaw moment is input thereto. In addition, as describedabove, since this test is carried out by the driver who performs thefree acceleration or deceleration in terms of the brake or theaccelerator, it is obvious that this embodiment is effective in thetransient acceleration or deceleration state of the vehicle.

When a close control is carried out by the driver, since the driverperforms an accurate control by using the brake, the steering, and theaccelerator, in many cases, the correction yaw moment is not necessary.In other words, when the control is carried out in such a case, anunpleasant feeling may increase. For this reason, in order to moreclearly verify the justification of the control logic (correction yawmoment calculation), it is verified whether the accurate correction yawmoment is calculated by performing an open loop test in which a steeringoperation is carried out left and right in a sine curve shape at apredetermined velocity.

FIG. 9 is a view illustrating a case where the reference yaw angularacceleration of the real vehicle obtained by dividing the lateralacceleration by the velocity is compared with the real yaw angularacceleration obtained by differentiating the yaw rate of the realvehicle when the steering operation is carried out in a sine curve shapeof 1 [Hz] by 40 [deg], 40 [deg], and 50 [deg] at vehicle velocities of20 [km/h], 60 [km/h], and 80 [km/h].

As it is generally known, the lateral motion performance (dynamics) ofthe vehicle varies in accordance with the vehicle velocity. The real yawangular acceleration has a low gain and a late phase when the vehiclevelocity is slow. The gain increases in accordance with the increase ofthe vehicle velocity, and thus a late degree of the phase appears to besmall (in fact, it is late). In such a case, the correction yaw momentneeds to vary in accordance with the vehicle velocity.

On the contrary, in the reference yaw angular acceleration, the steeringoperation, that is, the sine curve shape of 1 [Hz] stops and the phaseis not late in accordance with a Variation in velocity (this is becausethe vehicle dynamics are not used). Accordingly, although FIG. 10 showsthe correction yaw moment signal (ΔM) obtained from a difference betweenthe reference yaw angular acceleration and the real yaw angularacceleration, it is obvious that the correction amount includes avariation in dynamics with respect to the reference yaw moment.

SUMMARY

The control and the function of the motion control system for thevehicle according to the above-described embodiment are summarized asbelow. That is, in order to decrease the difference between the yawangular acceleration (r_real_dot) of the vehicle detected by the yawangular acceleration detecting means of the vehicle and the value(Gy_dot/V=r_ref_dot) (reference yaw angular acceleration) obtained bydividing the lateral jerk (Gy_dot) of the vehicle by the longitudinalvelocity (V) of the vehicle,

(1) the difference between the lateral forces of the front wheel and therear wheel is controlled by controlling the sideslip angles of therespective vehicle wheels of the vehicle,

(2) a drive or brake torque difference between the left and rightvehicle wheels is generated by controlling the longitudinal slip ratioof the respective vehicle wheels of the vehicle (in addition, it isgeneral to control the longitudinal slip ratio in order to varylongitudinal forces (front and rear forces) of the respective vehiclewheels, which was known in the past), and

(3) the difference between the lateral forces of the front and rearwheels varies in terms of the vertical load transfer between the frontand rear wheels due to the longitudinal acceleration.

Since the yaw moment of the vehicle is controlled by using the threemethods addition to a case where the three control methods areindividually applied, the control methods may be, of course, applied inan appropriate combination), it is possible to adjust the control yawmoment amount in accordance with a variation in dynamics of the vehicleincluding the transient acceleration or deceleration state of thevehicle, and thus it is possible to realize a safety driving. Simply, amain feature of the invention is that the yaw moment is controlled onthe basis of the difference between the real yaw angular acceleration(r_real) and the value (r_ref) obtained by dividing the lateral jerk ofthe vehicle by the longitudinal velocity by using the fact that thedivided value is the yaw angular acceleration (yaw moment is obtained bymultiplying the yaw angular acceleration by the yawing inertia momentIz) necessary for realizing the motion shown in FIG. 5.

Next, the motion control system for the vehicle according to anotherembodiment will be described herebelow. As shown in FIG. 7, in themotion control system according to the above-described embodiment, thefeedback control and the closed loop control based on the differencebetween the reference yaw angular acceleration and the real yaw angularacceleration of the vehicle are adopted.

On the contrary, in another embodiment, an open loop control,particularly, the yaw moment control in terms of the vertical loadtransfer is adopted. As described above, as disclosed in p. 54 to 60 of‘Improvement of Vehicle Motion Performance in terms of Yaw MomentControl’ published by ‘SOCIETY OF AUTOMOTIVE ENGINEERS OF JAPAN, INC.,Vol. 47, No. 12, 1993, within a range in which the lateral force of thetire is proportional to the load, the yaw moment (Mzls) due to theacceleration or deceleration during a steady state cornering action isproportional to a value obtained by the lateral acceleration by thelongitudinal acceleration as shown in Equation 22. Here, m denotes avehicle mass, h denotes a height of gravity center point, and g denotesa gravity acceleration.

$\begin{matrix}{M_{zls} = {{- \frac{mh}{g}}G_{x}G_{y}}} & \left\lbrack {{Equation}\mspace{14mu} 22} \right\rbrack\end{matrix}$Accordingly, when a necessary yaw moment is set to a value obtained bymultiplying a value (Gy_dot/V=r_ref_dot), obtained by dividing thelateral acceleration (Gy_dot) of the vehicle by the longitudinalvelocity (V) of the vehicle, by an inertia moment around a Z axis, thelongitudinal acceleration realizing the control moment having the sameprofile as that of the necessary yaw moment is obtained. This may beregarded as an overall control of longitudinal motion and lateral motionwhich determines the lateral acceleration generated by the steeringoperation and the longitudinal acceleration by the brake and acceleratoroperation in accordance with the lateral acceleration.

That is, this is a method for obtaining a value as an index for enablingthe system to automatically operate the brake and accelerator inaccordance with the driver's steering operation. When a proportionalconstant is denoted by c, a command longitudinal acceleration Gxc isexpressed as the following Equation 23.

$\begin{matrix}{{I_{Z}{\overset{.}{r}}_{ref}} = {{I_{Z}\frac{{\overset{.}{G}}_{y}}{V}} = {{c \cdot {- M_{zls}}} = {\left. {{- c}\frac{mh}{g}G_{xc}G_{y}}\Rightarrow G_{xc} \right. = {{- \frac{gIz}{cmhV}}\frac{{\overset{.}{G}}_{y}}{G_{y}}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 23} \right\rbrack\end{matrix}$When the brake and accelerator is controlled on the basis of the Gxcvalue, since the moment in terms of the load movement is generated to beclose to the reference yaw moment, the correspondence between therotation and the revolution is more improved, thereby improvingoperability and stabilizing the vehicle.

Upon being mounted to the vehicle and divided by the lateralacceleration (Gy) of the vehicle, in an initial turning state, in somecases, the lateral acceleration becomes a small value and the commandlongitudinal acceleration Gxc becomes a large value. In addition, thesame case may occur upon decreasing the speed. In order to avoid suchcases, as shown in Equation 24, it is sufficiently effective inpractical engineering even when the command longitudinal accelerationGxc is determined in such a manner that main information is obtainedfrom the lateral jerk (Gy_dot) of the vehicle and other information isobtained from the velocity, the lateral acceleration or the functionf(Gy, V) thereof, or dependent information and a gain KGyV stored in amap etc.G _(xc) =f(G _(y) ,V)·Ġ _(y) =K _(G) _(y) _(v) ·Ġ _(y)  [Equation 24]

Specifically, there are provided means for detecting the longitudinalvelocity (V) of the vehicle and the lateral jerk (Gy_dot) of thevehicle, and the longitudinal acceleration of the vehicle is controlledon the basis of the value (Gy_dot/V) obtained by dividing the lateraljerk (Gy_dot) of the vehicle by the longitudinal velocity (V) of thevehicle so that the yaw moment of the vehicle is controlled in terms ofthe vertical load transfer. More specifically, the lateral acceleration(Gy) of the vehicle is detected, and the longitudinal velocity of thevehicle is controlled on the basis of a physical value proportional to avalue obtained by dividing the value (Gy_dot/V), obtained by dividingthe lateral jerk (Gy_dot) of the vehicle based on the detection by thelongitudinal velocity (V) of the vehicle, by the lateral acceleration(Gy) of the vehicle so that the yaw moment of the vehicle is controlledin terms of the vertical load transfer between front and rear wheel.

While preferred embodiments has been described above, it should beunderstood, of course, that the invention is not limited thereto andvarious modifications or corrections can be made by those skilled in theart within the scope of the spirit of the invention and the appendedclaims.

What is claimed is:
 1. A motion control system for a vehicle comprising:a controller for controlling a yaw moment of the vehicle; a first sensorfor detecting a longitudinal velocity of the vehicle; and a secondsensor for detecting a lateral jerk of the vehicle, wherein thecontroller generates a control command for the yaw moment of the vehiclebased on a value obtained by dividing the lateral jerk of the vehicledetected by the second sensor, by the longitudinal velocity of thevehicle detected by the first sensor, the controller outputting thegenerated control command, and the controller controlling motion of thevehicle based on the generated control command.
 2. A motion controlsystem according to claim 1, wherein the controller calculates a yawangular acceleration based on a value obtained by dividing the lateraljerk of the vehicle by the longitudinal velocity of the vehicle, and thecontroller generating a control command for the yaw moment of thevehicle based on the yaw angular acceleration.
 3. A motion controlsystem according to claim 2, wherein the controller generates a controlcommand for the yaw moment of the vehicle based on the yaw angularacceleration and a real yaw angular acceleration of the vehicle.
 4. Amotion control system according to claim 2, wherein the controllergenerates a control command for the yaw moment of the vehicle based onthe yaw angular acceleration and a driver's input value.
 5. A motioncontrol system according to claim 4, wherein the driver's input valueincludes at least any one of steering operation information, left andright differential brake and drive information, or load movement fromrear wheel to front wheel information.
 6. A motion control system for avehicle comprising: a controller for controlling a yaw moment of thevehicle, wherein the controller generates a control command for the yawmoment of the vehicle based on a value obtained by multiplying a lateraljerk of the vehicle by a prestored gain, the controller outputting thegenerated control command, and the controller controlling motion of thevehicle based on the generated control command.
 7. A motion controlsystem according to claim 6, wherein the controller calculates a yawangular acceleration based on a value obtained by dividing the lateraljerk of the vehicle by the longitudinal velocity of the vehicle, and thecontroller generating a control command for the yaw moment of thevehicle based on the yaw angular acceleration.
 8. A motion controlsystem according to claim 7, wherein the controller generates a controlcommand for the yaw moment of the vehicle based on the yaw angularacceleration and a real yaw angular acceleration of the vehicle.
 9. Amotion control system according to claim 7, wherein the controllergenerates a control command for the yaw moment of the vehicle based onthe yaw angular acceleration and a driver's input value.
 10. A motioncontrol system according to claim 9, wherein the driver's input valueincludes at least any one of steering operation information, left andright differential brake and drive information, or load movement fromrear wheel to front wheel information.